Previous studies have demonstrated that the outer membrane of Treponema pallidum is physically labile and has the ability to resist binding of specific antibody. It is hypothesized that these properties are the result of a paucity of integral membrane proteins in the outer membrane and that the resistance to binding specific antibody constitutes a major treponemal defense against the host humoral immune response. Phase partitioning with the nonionic detergent Triton X-114 has been used to identify a group of pathogen-specific, putative integral membrane proteins (detergent-phase proteins) in T. pallidum. Among the detergent- phase proteins (DPPs) are several previously unrecognized and/or poorly characterized antigens, including 15- and 17-kDa polypeptides which are extremely immunoreactive with human syphilitic serum. Murine monclonal antibodies will be raised against the DPPs, and individual proteins within the detergent phase will be purified. Monoclonal and polyclonal antibodies generated against these proteins will be used to determine their precise intracellular locations by immunocytochemical localization on ultrathin cryosections and by analysis of isolated intact outer and cytoplasmic membranes. Freeze-fracture electron microscopy will be performed as an alternative method for determining the relative protein contentts of the outer and cytoplasmic membranes. Structure-function analysis of DPPs will be performed to identify biologically significant structural domains. Proteolytic digests of DPPs will be examined by immunoblotting and by solid-phase immunoassy using monoclonal and polyclonal antibodies. Antibodies to DPPs will be assayed for biological activity against virulent T. pallidum. The 15- and 17- kDa DPPs, which are quantitatively minor components of the detergent-phase mixture, will be cloned and expressed in E. coli. The proposed studies will provide new insights into T. pallidum ultrastructure, into the organism's host-parasite relationships, and into the contributions of newly characterized membrane proteins to the complex immunopathology of syphilis.